Serban D. Porumbescu

Ph.D.

email: idav 'at' hiddenelephant.com

Hello and welcome to my research page. My name is Serban (pronounced Sir-Bon) Porumbescu (pronounced Pour-oom-bess-coo).
I completed my PhD in 2005. During my studies, my research was primarily focused on 2D
surface parameterization and remeshing of large data.
Some of my most interesting results involve 3D near surface parameterizations
(see Shell Maps below). Ken Joy was my advisor.

After graduating in 2005, I spent some time at Sony R&D, NVIDIA, and my own little startup that focused on work in the nonprofit sector. In October 2008 I started a new company, Hidden Elephant, focused on iPhone application development.

I joined iPhone startup Tapulous in
October of 2009 as a senior gameplay engineer. While there I worked on a
number of different projects (two that come to mind: Tap Tap Radiation and
Riddim Ribbon). That Fall I also designed and taught UCD's first iPhone development
course with Ken Joy.
I left Tapulous in September of 2010, two months after we were acquired by Disney, to focus on my own indie development projects.

In November 2010 my company, Hidden Elephant, partnered with Limbic Software.
Together we developed the hit iOS game, Zombie Gunship (released July, 2011).
I spent the rest of 2011 and big chuncks of 2012 adding features and updating Zombie Gunship.

Geometric Texturing Using Level Sets

Anders Brodersen,
Ken Museth,
Serban Porumbescu,
Brian Budge

IEEE Transactions on Visualization and Computer Graphics 2008

We present techniques for warping and blending (or
subtracting) geometric textures onto surfaces represented by high
resolution level sets. The geometric texture itself can be
represented either explicitly as a polygonal mesh or implicitly as a
level set. Unlike previous approaches, we can produce topologically
connected surfaces with smooth blending and low distortion.
Specifically, we offer two different solutions to the problem of
adding fine-scale geometric detail to surfaces. Both solutions
assume a level set representation of the base surface which is
easily achieved by means of a mesh-to-level-set scan conversion. To
facilitate our mapping, we parameterize the embedding space of the
base level set surface using fast particle advection. We can then
warp explicit texture meshes onto this surface at nearly interactive
speeds or blend level set representations of the texture to produce
high-quality surfaces with smooth transitions.

Shell
Maps

ACM SIGGRAPH 2005

A shell map is a bijective mapping between shell space and texture space that can be used to generate small-scale features on surfaces using a variety of modeling techniques. The method is based upon the generation of an offset surface and the construction of a tetrahedral mesh that fills the space between the base surface and its offset. By identifying a corresponding tetrahedral mesh in texture space, the shell map can be implemented through a straightforward barycentric-coordinate map between corresponding tetrahedra. The generality of shell maps allows texture space to contain geometric objects, procedural volume textures, scalar fields, or other shell-mapped objects.

Meshless Isosurface
Generation from Multiblock Data

Christopher S. Co, Serban D.
Porumbescu, Kenneth I. Joy

VisSym 2004

We propose a meshless method
for the extraction of high-quality continuous isosurfaces from
volumetric data represented by multiple grids, also called multiblock
data sets. Multiblock data sets are commonplace in computational
mechanics applications. Relatively little research has been performed
on contouring multiblock data sets, particularly when the grids overlap
one another. Our algorithm proceeds in two steps. In the first step, we
determine a continuous interpolant using a set of locally defined
radial basis functions (RBFs) in conjunction with a partition of unity
method to blend smoothly between these functions. In the second step,
we extract isosurface geometry by sampling points on Marching Cubes
triangles and projecting these point samples onto the isosurface
defined by our interpolant. A surface splatting algorithm is employed
for visualizing the resulting point set representing the isosurface.
Because of our method's generality, it inherently solves the crack
problem in isosurface generation. Results using a set of synthetic data
sets and a discussion of practical considerations are presented. The
importance of our method is that it can be applied to arbitrary grid
data regardless of mesh layout or orientation.

Dataflow and Remapping for Wavelet Compression and View-dependent Optimization of Billion-Trangle Isosurfaces

Currently, large physics simulations produce 3D discretized field data whose individual isosurfaces, after conventional extraction processes, contain upwards of hundreds of millions of triangles. Detailed interactive viewing of these surfaces requires (a) powerful compression to minimize storage, and (b) fast view-dependent optimization of display triangulations to most efectively utilize high-performance graphics hardware. In this work, we introduce the first end-to-end multiresolution data flow strategy that can effectively combine the top performing subdivision-surface wavelet compression and view-dependent optimization methods, thus increasing efficiency by several orders of magnitude over conventional processing pipelines. In addition to the general development and analysis of the data flow, we present new algorithms at two steps in the pipeline that provide the "glue" that makes an integrated large-scale data visualization approach possible. A shrink-wrapping step converts highly detailed unstructured surfaces of arbitrary topology to the semi-structured meshes needed for wavelet compression. Remapping to triangle bintrees minimizes disturbing "pops" during realtime display-triangulation optimization and provides effective selective-transmission compression for out-of-core and remote access to extremely large surfaces. Overall, this is the first effort to exploit semi-structured surface representations for a complete large-data visualization pipeline.

Peer Timo Bremer, Serban D. Porumbescu, Bernd Hamann, Kenneth I. Joy

Curve and Surface Fitting: Saint-Malo 2002

This paper describes a method to construct semi-regular meshes for a surface S defined by the zero set of a trivariate function F(x,y,z), representing a distance field definition of S. An adaptive distance field (ADF) definition of S is obtained by constructing, adaptively, an octree decomposition of F's domain. The vertices of the octree-based definition of S lie either on the positive or negative side of S (or on S). Octree cells that are intersected by S are identified, and the faces of these cells that lie on the outside of S are projected onto S. The result is a quadrilateral mesh to which various procedures are applied that lead to an improved mesh containing a much smaller number of extraordinary vertices, i.e., non-valence-four vertices.

This paper describes an approach for the parametrization and modeling of objects represented by adaptive distance fields (ADFs). ADFs support the construction of powerful solid modeling tools. They can represent surfaces of arbitrary and even changing topology, while providing a more intuitive user interface than control-point based structures such as B-splines. Using the octree structure, an adaptively refined quadrilateral mesh is constructed that is topologically equivalent to the surface. The mesh is then projected onto the surface using multiple projection and smoothing steps. The resulting mesh serves as the ``interface'' for interactive modeling operations and high-quality rendering.

Interactive Display of Surfaces Using Subdivision Surfaces and Wavelets

Complex surfaces and solids are produced by large-scale modeling and simulation activities in a variety of disciplines. Productive interaction with these simulations requires that these surfaces or solids be viewable at interactive rates Ð yet many of these surfaces/solids can contain hundreds of millions of polygons/polyhedra. Interactive display of these objects requires compression techniques to minimize storage, and fast view-dependent triangulation techniques to drive the graphics hardware. In this paper, we review recent advances in subdivision-surface wavelet compression and optimization that can be used to provide a framework for both compression and triangulation. These techniques can be used to produce suitable approximations of complex surfaces of arbitrary topology, and can be used to determine suitable triangulations for display. The techniques can be used in a variety of applications in computer graphics, computer animation and visualization.